Thanks for all the replies. Wow! This is very interesting.
I do ask my kids to write personal notes for the teachers, and I do feel a bit of pressure to donate to the gift fund. At the school my kids attend, you only get to sign the card if you donate. It seems like it's almost public shaming as a way of forcing people to donate.
I suspect that the people collecting the money wouldn't see it this way, though. I can imagine that from their perspective, you shouldn't be allowed to sign the card if you didn't make a donation. They're trying to be nice and probably don't see that there's another side to their actions.
